Nano-imprint lithography (NIL) is a type of micro-fabrication technique that is becoming increasingly important in semiconductor processing and other applications. Imprint lithography provides greater process control and reduction of the minimum feature dimension of the structures formed. This in turn provides higher production yields and more integrated circuits per wafer, for example. Nano-imprint lithography can be used to form a relief image on a substrate, such as a semiconductor wafer. Nano-imprint lithography has two basic steps. The first step is imprint step in which a mold with a relief nanostructure on its surface is pressed into a thin resist film cast on to a substrate, followed by the removal of the mold.
Unlike conventional lithography methods, imprint lithography itself does not use any energetic beams. Therefore, nano-imprint lithography's resolution is not limited by the effects of wave diffraction, scattering and interference in a resist, and backscattering from a substrate. Imprint lithography systems often use an imprint head with a mold, also called a template, which can be installed and removed from the imprint head. This allows the imprint lithography system to be used to imprint different patterns. In this manner, the imprint lithography system can be used to fabricate various types of circuits or other devices, or imprint various structures on a substrate.
Nano-imprint lithography (NIL) has been identified as a possible candidate in realizing the 32-nm technology node in the semiconductor industry. The potential for NIL largely depends upon the ability of its proponents to demonstrate a faultless industrial implementation in all aspects. One such aspect that has acquired a rather sizable dimension in the early investigations is the issue of managing the NIL templates for contamination, pattern fidelity and longevity during production use.
Embodied within the concept of template contamination and pattern fidelity are all the attempts to generate a pattern surface free of particulate contamination as well as providing surface properties to template to ensure clean release after the imprinting. Similarly embodied within the concept of template longevity are all the attempts to maintain the continuous utilization of a template in a production environment, while maintaining the quality of the product within given specifications. Given that nano-imprint lithography is still an emerging technology; there are few standard procedures to achieve any of the goals described above.
The templates used in nano-imprint lithography require frequent periodic cleaning. Conventionally, these templates have been cleaned for first use by spraying them with sulfuric acid (H2SO4) followed by Nitrogen blow drying. To reclaim a template after use it is often necessary to remove contamination that occurs during production runs. Current methods of reclaiming a template after contamination during production runs involve repeating the wet chemical cleaning and manual surface treatment for release characteristics. Unfortunately, such wet cleaning can be expensive to implement, involves hazardous and corrosive chemicals that must be disposed of somehow. Disposal of such chemicals presents an environmental hazard that adds to the overall expense of wet chemical cleaning in particular and nano-imprint lithography in general.
Water soluble polymers have been used to clean optical surfaces. The film is spun on to an optical surface in liquid form, air dried and then peeled off. As the film is peeled off, inorganic particles and other contaminants on the optical surface stick to the film and are removed. Unfortunately after the film is removed an organic residue remains on the surface. It has been suggested that the residue may be removed by baking the optical surface, e.g., at about 250° C. Unfortunately, such baking may not sufficiently remove the organic residue. In addition, some optical surfaces, such as semiconductor wafers, photomasks and imprint templates would warp or be otherwise damaged by heating. If the film is water soluble, the residue could potentially be removed by rinsing in de-ionized water. However, a water rinse is usually not enough. A water rinse would typically need to be followed by drying with an alcohol vapor. This sequence of wet processing is typical, but involves quite a bit of equipment, as well as fire, and health hazards.
Organic solvents are typically used in the template manufacturing process to remove films such a photoresist after the patterning is finished. The solvents are used to dissolve the resist film, but the surface may require additional cleaning to remove any residues from the solvent resist stripping.
Thus, there is a need in the art, for a method for cleaning optical surfaces that overcomes the above drawbacks.